Oscillation generator



Feb. 11, 1941. F. H. SHEPARD JR OSCILLATION GENERATOR Filed Oct. 16, 1937 4 Sheets-Sheet 2 MODULATION IN PU T 8 .2 T 6 3 LT n u 2% E? INVENTOR. FRANCIS H. fl/EPARQJE ATTORNEY.

Feb. 11, 1941. v H SHEPARD, JR 2,231,687

OSCILLATION GENERATOR Filed Oct. 16, 1937 4 Sheets-Sheet 3 TO U TIL IZA T/ON CIRCUIT llll 70 U 7' /L /ZA 7' ION CIRCUIT INVENTOR. FRAN l6 H. SHEPARQJR.

ATTORNEY.

Feb. 11, 1941,

F. H. SHEPARD, JR 2,231,687

OSCILLATION GENERATOR Filed Oct. 16, 1937 4 Sheets-Sheet 4 :?E 8 x i fi 4 ll 4 u 3 /n J F 43 I 4 /2 MIC 42 ATTORNEY.

Patented Feb. 11, 1941 UNITED STATES PATENT OFFICE OSCILLATION GENERATOR tion of Delaware Application October 16, 1937, Serial No. 169,362

25 Claims.

The present invention relates to self-excited thermionic oscillator circuits in which the amplitude of self-oscillation is regulated or controlled by means of variation of the mutual conductance of the thermionic device therein.

The objects of this invention are: To provide a method of and circuit arrangement for maintaining the output voltage of an evacuated electrical oscillation generator tube substantially in proportion to, or, if desired, independent of variations of any of the supply voltages and of the characteristics of the tube; to reduce the production of harmonic frequencies in a modulated oscillator; to increase the frequency stability by reducing the effect of the damping of the tube characteristics on the associated resonant circuits; to provide a simple method of regulating the intensities of an oscillator over a wide range of load and circuit variations; to provide, in a self-excited oscillator tube, a method of and circiut arrangement for automatically varying the grid bias of a mutual conductance controlling grid other than the oscillator grid, as a function of the ampltiude of oscillations.

In the present invention the oscillator output, with or without amplification, is rectified, and a part or all of the direct current voltage to this rectification is fed back through a filternetwork and, if desired, this voltage or the resultant voltage fed through a direct current amplifier to one of the other grids of the oscillator. In this way, the feed-back voltage controls the mutual conductance of the oscillator in accordance with the direct current voltage developed from the oscillator output.

One advantage of the present invention lies in operating the oscillator as Class A, with only thehigh impedance part of the tube characteristic damping the tank circuit, in order that a large percentage of modulation in theoscillator output can be obtained from relatively small modulation voltages applied to the mutual conductance controlling grid. This is due to the fact that a small variation of the mutual conductance of an oscillator having high plate impedance and operating Class A will result in a. large variation of oscillation intensity.

Other objects, features and advantages will appear in the following description which is accompanied by drawings wherein like reference numerals indicate like parts. In these drawings:

Fig. 1 shows a particular embodiment of an oscillator circuit employing a thermionic pentagrid tube operating as a Class A generator in which the negative control voltage applied to the mutual conductance controlling grid (#3 grid) is derived from the direct current voltage developed by the oscillator grid (#1 grid) Fig. 2 is another embodiment of the invention similar to that shown in Fig. 1, with the exception that the plate or anode end of the oscillator circuit is grounded for the oscillator frequency;

Fig. 2a is substantially the same as Fig. 2, with the exception that a fixed direct current bias is .used in series with the rectified voltage to the mutual conductance controlling grid;

Fig. 3 is substantially the same circuit as shown in Fig. 1 except that the grid is grounded for radio frequency energy;

Fig. 4 is similar to Fig. 3, except that an oscillator tube with a smaller number of grids is employed;

Fig. 5 shows an embodiment of the invention in which the oscillator is used as a self-balancing capacity-operated relay to transmit carrier frequencies over a power line to some suitable utilization circuit;

Fig. 6 shows a still further embodiment of the invention wherein the output voltage is externally amplified and then rectified in a separate diode before being fed back to the mutual conductance controlling grid of the oscillator tube;

Figs. '7 and 8 illustrate circuit arrangements embodying the principles of the invention, which may be used as stable capacity operated alarms in which the regulatory action is delayed to give high sensitivity to relatively high speed feed-back variations to the oscillator;

Fig. 9 is another embodiment of the invention in which the oscillator is stabilized against slow feed-back variations, but not against high speed feed-back variations; and

Fig. 10 shows a modification in which the mutual conductance of the oscillator tube is controlled by the regulation of electron emission from the cathode due to a controlling of the temperature of the cathode.

Although the invention is hereinafter described with particular reference to oscillator tubes functioning Class A, that is, tubes which are conductingat all times, it should be understood that the invention is not limited thereto.

Referring to the drawings and to Fig. 1 in particular, there is shown a pentagrid oscillator tube I whose anode 2, first grid 3, and cathode 4 are connected to a tank circuit 5 in themanner of the well-known Hartley circuit. C'onductively connected to the first grid 3 of the tube and to the cathode is a grid leak resistance 6 across which a direct current voltage is developed in a manner known to those familiar with the art. This direct current voltage is fed via a tap II through a filter comprising, for example, a resistance 1, an inductance 8, and another resistance 9 back to the third grid ID of the oscillator I in order to control the mutual conductance of the tube. Inductance 8 is connected to resistance at junction point I5. The filter may be said to include a condenser I2 which by-passes the oscillator frequency from the grid III to the cathode.

In operation, the tube I acts as follows: A part of the direct current voltage developed on grid 3 is picked up by the slider II on resistor 6 and fed through resistor I, inductance 8, and resistance 9 to grid IQ of the oscillator. Any oscillator frequency component of voltage that may appear on this grid is effectively filtered to the cathode 4 by means of the oscillator frequency by-pass condenser I2. The negative voltage thus applied to grid I6 is effective in controlling the mutual conductance of the oscillator tube I in such a manner that a balance is maintained between the intensity of oscillation and the negative voltage on grid It. It is to be noted that the amplitude of oscillation can be of such low value that tube I conducts anode current over all parts of the cycle. Due to the fact that the tube impedance which is shunted across part of the tank circuit 5 is essentially infinite, its damping effect on the tank circuit 5 can be considered to be negligible. This means that the variation in this abovementioned (tube impedance) load on the tuned circuit will have a negligible efiect on the frequency stability of the tuned circuit itself. Where desired, a source of relatively low frequency modulation (shown, for example, in conventional manner by the box I4) may be applied through a suitable condenser I3 to the grid I0, as illustrated.

One advantage of this arrangement is that the direct current voltage developed from the oscillator output and applied to the grid ID of the oscillator will be unaffected by the modulation voltage applied to this same grid by source l4. Furthermore, the speed at which this direct current voltage can be applied through impedance "I to the junction point I5 is limited by the time constant between impedance 1 and condenser I3. This time constant is also determined by the value of condenser I2, choke 8 and resistor 9. Thus the modulation input from source I 4 does not affect the average output oscillation intensity. However, alternating current modulating voltage appearing across impedance I is fed through choke 8, resistance 9, across condenser I2, into the grid I 0. As this relatively low frequency alternating current voltage is efiective in modulating the mutual conductance of the oscillator tube I, the output oscillation intensity is likewise modulated. Thus a small modulation input voltage is effective in producing a relatively large percentage of variation of the oscillator output. This is because a relatively large amplitude variation of oscillation is initiated by a relatively small variation of the mutual conductance of the oscillator I and because a relatively large variation of mutual conductance is occasioned by a relatively small variation of the instantaneous voltage on grid I0.

Fig. 2 is substantially the same as the circuit shown in Fig. 1, with the exception that a different point on the anode side of the tank circuit 5 is grounded. The system of Fig. 2 operates in the same manner as that of Fig. l, for which reason the description given above for Fig. 1 applies to Fig. 2. There is, however, a slight modification in the filter circuit of Fig. 2, although if desired the same type of filter circuit shown in Fig. I may be employed. For the sake of simplicity of the drawings, the relatively low frequency modulation source of Fig. 1 has been omitted from Fig. 2. It should be observed that whereas in Fig. 1 the anode 2 is directly connected to one terminal of the tank circuit 5, in Fig. 2 the anode 2 is connected for the oscillator frequency to the same terminal of the tank through the by-pass condenser I6.

Fig. 2a shows substantially the same circuit as Fig. 2 with the exception that a fixed direct current bias source 58 is used in series with the rectified voltage fed back to the mutual conductance controlling grid I0.

Fig. 3 shows a circuit which is similar to that of Fig. 1, with the exception that the tank circuit 5 is grounded for the oscillator frequency at the end which is connected through the power supply condenser SI, and connected through the combination of grid leak I1 and grid condenser I8 to the grid 3 of the oscillator tube I.

Fig. 4 shows a circuit which is similar to that of Fig. 3, with the exception that a three-grid oscillator tube I' is used instead of the pentagrid oscillator tube I previously referred to. In this figure the prime designations on the electrodes of the tube are intended to designate elements of the tube which correspond in function to the elements of the tube of Fig. 3 without the prime designations. The condenser and coil of tank 5 are here labeled 52 and 54, respectively, and the upper terminal of tank 5 labeled 53 for purposes which will appear hereinafter. The operation of Fig. 4 is the same as that hereinabove described.

Fig. 5 shows an oscillator similar to the oscillator shown in Fig. 4, with the exception that the tank circuit 5 of Fig. 4 has been modified so that the condenser 52 is connected to the terminal 53 of the coil 54 through the impedance medium of the power supply. In other words, one electrode of condenser 52 is connected to the lower side of the power supply instead of the upper side, as shown in Fig. 4, in such a way that energy at oscillator frequency is fed onto the power supply line. An antenna 55 is connected to the oscillator grid 3 to make the intensity of output sensitive to variations in the antenna to ground capacity. The voltage on the first grid 3 is modified by the effects of the capacity divider which consists of the antenna to ground capacity 2I, shown in dotted lines, and the capacity 22 placed between the grid 3' and the anode 2' of the tube.

The system of Fig. 5 can be used as shown, to feed control energy into a carrier operated relay placed somewhere else on the power line, as shown. The oscillation intensity is controlled, as explained, by the antenna to ground capacity in such a way that momentary variations result in relatively large oscillation intensity variations which are fed over the power line to operate the relay. The system of Fig. 5 may be used as an effective burglar alarm system. It will be appreciated, of course, that the antenna 55 shown in Fig. 5, as well as in Figs. '7 and 8 to be described hereinafter, is not limited to a rod capable of radiating waves, but may be any suitable capacity surface.

Fig. 6 shows a modification of the circuit of Figs. 1 and 2, in which the oscillator I is used as a signal generator to supply an essentially constant amplitude output signal of widely varying frequency. The oscillator of this circuit is substantially identical to the circuit shown in Fig. 2, with the exception that the negative direct current voltage applied to grid I0 is derived by the rectifying action of the diode 23 which, in turn, is driven, as shown, by the buffer stage 24. In the operation of this circuit, oscillations generated as described above in connection with Figs. 1 and 2 are fed directly from the tank circuit 5 to the first grid 25 of the buffer stage 24, thereby causing a like voltage to appear across the cathode resistor 26 of this buffer tube. This resistor 26 may comprise a part of an attenuating network 21 which can be calibrated in terms of the voltage between the slider 28 on resistor 26 and ground. The oscillator frequency voltage appearing on the cathode 28 of the buffer tube 24 is fed through coupling condenser 29 to the anode 30 of diode 23, thus causing a rectified voltage to be built up across the diode load resistor 3|. A part or a whole of this direct current voltage is picked up by the slider 32 and fed through the resistor 1' and choke coil 8' to the grid I0 of the oscillator l. The constants of the circuit are so designed that the time constant formed by resistor l and condenser I3 is such that no audio frequency component can be passed from the slider 32 to point I5 into the grid in of the oscillator (this assumes that the modulation input has relatively low impedance with respect to resistor 1'). If desired, a modulation input having a frequency high with respect to the above-mentioned time constant may be fed in, as shown, through condenser l3, choke 8' across condenser l2 into the grid. It of the oscillator, thus causing a modulation of oscillation intensity as described above in connection with Figs. 1 and 2. As the direct current rectified by the diode 23 is a direct function of the intensity of oscillation, a direct current meter 33 arranged to measure the direct current passed by the diode can be used to indicate directly the amplitude of oscillation. The buffer tube 24 serves to isolate the diode load and the attenuator load from the oscillator circuit proper.

Fig. 7 shows a circuit in which the oscillator is used as a burglar alarm sensitive to capacity variations in the same manner as is the circuit of Fig. 5. It is to be noted that the oscillator of this circuit is essentially similar to the oscillator shown in Fig. 2, with the exception that the voltage on the grid 3 is modified by the capacity divider formed by the antenna to ground capacity 34, shown in dotted lines, and the condenser 35. The negative voltage which is applied to the grid I0 ofthe pentagrid oscillator tube I is derived from the diode which includes the cathode 35 and anode-grid 3'! of a tube 38. This negative voltage which is on. the anode 31 of this diode is built up across condenser 39 and resistor 48 and is applied through resistor H to the grid if) of the oscillator tube I. It is to be noted that the intensity of oscillation is indicated on the upper half of the power cycle by the effect of the direct current potential of the grid 31 on the plate current conducted through the tube 38 during the interval that its anode and screen volages are positive. By this is meant that the oscillator tube 1 cscillates on one-half of the alternating current power cycle during which the above-mentioned negative voltage is built upon the grid 37. On the following half cycle. the oscillator anode and screen voltages are driven negative with respect to the oscillator tube cathode, and the plate and screen voltages of the output tube 38 are drawn positive, and the negative voltage built up on the grid 31 is effective in controlling the plate current of the tube 33. This plate current can be used to operate a relay st or other output indicating device, as shown.

Fig. 8 shows a circuit essentially identical to that shown in Fig. 7, with the exception that a three-grid oscillator tube I is used in place of the pentagrid oscillator tube shown in Fig. 7. In this Fig. 8 a tetrode 4| is used instead of the pentode 38 shown in Fig. 7. The operation of Fig. 8 is substantially the same as that of Fig. 7.

Fig. 9 is a circuit in which the high dynanrrlc sensitivity of the oscillator to variations in the feed-back are utilized to control the output the oscillator in accordance with. the variations of the capacity of a condenser microphone 42. The oscillator of the circuit shown in Fig. 9 is essentially the same as the oscillator shown in Fig. 2, with the exception that the grid potential is modified by the capacity divider which is formed by the condenser microphone ti! and the condenser 43. The direct current voltage developed on the grid 3 is fed through the filter network comprising an inductance 8 and a resister 9 to the grid N3 of the oscillator. It is to be noted here that the time constant formed by condenser I2 and the impedance of d, 9 such that it is long with respect to any modulation frequency or any voice frequency impinged upon the condenser microphone 472. Thus the amplitude of the oscillator is modulated in accordance with the capacity variations of the condenser microphone 42, and direct current voltage appearing on the grid 3 is likewise modulated. The modulated direct current voltage is fed through the choke 44 across condenser 45 into the grid of an output amplifier stage -45. Choke M and condenser 45 serve to prevent the voltage on the grid 3 from being fed to the output amplifier cs.

Fig. 10 shows another embodiment of the in vention similar to all of the Figures (1 to 9, inclusive), in that the amplitude of oscillation of the oscillator is controlled by the control of mutual conductance of the oscillator. In this case, the mutual conductance of the oscillator tube 41 is controlled by the heater current passing through its cathode 51. This heater current is, in turn, regulated by the action of the thermionic tube 48 which acts as a grid leak detector. In other words, oscillator voltage applied to the grid 49 of the tube 48 results in a negative potential being built up across the load resistor 50 which, in turn, reduces the plate current passed by the tube 48. As the plate current of this tube is used to heat the cathode of tube 4?, it can be seen that as the plate current of tube 48 is reduced so is the heater current or emission current or mutual conductance of tube 41 reduced.

It will be understood that the present invention is not limited to the precise arrangements of circuit illustrated since various modifications may be made without departing from the spirit and scope of the invention.

What is claimed is:

1. A self-excited oscillator circuit in which the amplitude of oscillations is controlled, comprising an electron discharge device having an anode electrode, a grid electrode, and a cathode electrode; a tuned circuit coupled to said electrodes in such manner as to produce oscillations; a circuit coupled to said cathode and one of said other electrodes for developing a direct current voltage from the produced oscillations in said tuned circuit; means including another electrode in the path of the electron stream and a filter connected between said other electrode and said last circuit for controlling the mutual conductance of said device from a portion at least of said direct current voltage; and means connected between said mutual conductance controlling electrode and said cathode for by-passing any oscillator frequency component of voltage which may appear on said electrode.

2. A self-excited oscillator circuit in which the amplitude of oscillations is controlled, comprising an electron discharge device having an anode, an oscillator grid, an auxiliary grid, and a cathode; a tuned circuit coupled to said anode, oscillator grid, and cathode for producing oscillations; a circuit coupled to said cathode and oscillator grid for developing a direct current voltage from the produced oscillations; and a feed-back path including a filter from said last circuit to said auxiliary grid to control the mutual conductance of said device in accordance with the direct current voltage developed in said last circuit, and a path of low impedance for the oscillator frequency connected between said auxiliary grid and said cathode.

3. A self-excited oscillator circuit in which the amplitude of oscillations is controlled, comprising an electron discharge device having an anode, an oscillator grid, an auxiliary grid, and a cathode; a tuned circuit having one terminal coupled to said anode, another terminal coupled to said oscillator grid, and an intermediate terminal thereon coupled to said cathode to produce oscillations; and means for rectifying a portion of the energy produced in said tuned circuit and feeding back the recified energy to said auxiliary grid to control the mutual conductance of said device, said means including a filter having a resistance connected in series in a path extending from said auxiliary grid to said oscillator grid.

4. A self-excited oscillator circuit in which the amplitude of oscillations is controlled, comprising an electron discharge device having an anode, an oscillator grid, an auxiliary grid, and a cathode; a tuned circuit having one terminal coupled to said anode, another terminal coupled to said oscillator grid, and an intermediate terminal thereon coupled to said cathode to produce oscillations; a resistance connected between said oscillator grid and a point of relatively fixed radio frequency potential for developing a direct current voltage therein; and an electrically conductive connection including an impedance between a point on said resistance and said auxiliary grid for feeding back a portion of the developed direct current voltage, whereby the mutual conductance of said device is controlled in accordance with said voltage.

5. A self-excited oscillator circuit in which the amplitude of oscillations iscontrolled, comprising an electron discharge device having an anode, an oscillator grid, an auxiliary grid, and a cathode; a tuned circuit having one terminal coupled to said anode, another terminal coupled to said oscillator grid, and an intermediate terminal thereon coupled to said cathode to produce oscillations; a resistance connected between said oscilaltor grid and a point of relatively fixed radio frequency potential for developing a direct current voltage therein; an electrically conductive connection between a point on said resistance and said auxiliary grid for feeding back a portion of the developed direct current voltage, whereby the mutual conductance of said device is controlled in accordance with said voltage; and a filter comprising an impedance inserted in said connection.

6. A self-excited oscillator circuit in which the amplitude of oscillations is controlled, comprising an electron discharge device having an anode, an oscillator grid, an auxiliary grid, and a cathode; a tuned circuit having one terminal coupled to said anode, another terminal coupled to said oscillator grid, and an intermediate terminal thereon coupled to said cathode to produce oscillations; said device having an anode current impedance characteristic which is extremely high; means for applying polarizing potentials to the electrodes of said device of such value that anode current flows through said device throughout a complete cycle of oscillations; means for rectifying a portion 01 the energy produced in said tuned circuit and feeding back the rectified energy to said auxiliary grid to control the mutual conductance of said device; said oscillator being so arranged that only its high impedance part of the tube characteristic damps said tuned circuit; and a condenser connected between said auxiliary grid and said cathode for by-passing any oscillator frequency component of voltage which may appear on said last grid.

7. A self-excited oscillator circuit in which the amplitude of oscillations is controlled, comprising an electron discharge device having an anode, an oscillator grid, an auxiliary grid, and a cathode; a tuned circuit having one terminal coupled to said anode, another terminal coupled to said oscillator grid, and an intermediate terminal thereon coupled to said cathode to produce oscillations; said device having an anode current impedance characteristic which is extremely high; means for applying polarizing potentials to the electrodes of said device of such value that anode current fiows through said device throughout a complete cycle of oscillations; a resistance connected between said oscillator grid and a point of relatively fixed radio frequency potential for developing a direct current voltage therein; a connection between a point on said resistance and said auxiliary grid for feeding back a portion of the developed direct current voltage, whereby the mutual conductance of said device is controlled in accordance with said voltage; and a filter having a predetermined time constant inserted in said connection.

8. A system in accordance with claim 5, in cluding a source of relatively low frequency alternating current voltage coupled to said connection for modulating the oscillations produced by said oscillator, whereby a small modulating voltage is effective in producing a large percentage of variation in the output of said oscillator.

9. A self-excited oscillator circuit comprising an electron discharge device having an anode, a cathode, and first, second and third grids; a source of voltage supply conductively connected between said anode and cathode, a tuned circuit coupled to said anode, cathode and first grid in such manner as to produce oscillations; said tuned circuit having a coil connected between said anode and one side of said voltage supply, and a condenser connected between said anode and the other side of said voltage supply; a connection from said second grid to a point on said coil intermediate its ends; a resistance connected between said first grid and a point of substantially fixed radio frequency potential; an antenna coupled to said first grid, a conductive connection including an impedance from said resistance to said third grid, whereby the mutual conductance of said device is controlled in accordance with the direct current voltage developed on said first grid and the intensity of oscillations controlled by the capacity between said antenna and said point of fixed radio frequency potential.

10. A self-excited oscillator circuit comprising an electron discharge device having an anode, a cathode, and first, second and third grids; a source of voltage supply conductively connected between said anode and cathode, a tuned circuit coupled to said anode, cathode and first grid in such manner as to produce oscillations; said tuned circuit having one terminal coupled to said first grid, another terminal coupled to said anode, and an intermediate terminal coupled to said cathode for producing oscillations; a resistance connected between said first grid and cathode; an antenna coupled to said first grid; a connection from said second grid to said cathode; and means for rectifying a portion of the oscillations produced in said tuned circuit and feeding said rectified portion back to said third grid for controlling the mutual conductance of said device.

11. A system in accordance with claim 10, characterized in this that said means includes a separate tube, one of whose electrodes is coupled to said tun-ed circuit and another of whose electrodes is coupled through a time constant circuit to said third grid.

12. A self-excited oscillator circuit in which the amplitude of oscillations is controlled, comprising an electron discharge device having an anode, an oscillator grid, an auxiliary grid, and a cathode; a tuned circuit having one terminal coupled to said anode, another terminal coupled to said oscillator grid, and an intermediate terminal thereon coupled to said cathode to produce oscillations; and means for rectifying a portion of the energy produced in said tuned circuit and feeding back the rectified energy to said auxiliary grid to control the mutual conductance of said device, said means including a filter having an inductance in series with a resistance connected between said auxiliary grid and said oscillator grid.

13. A self excitcd oscillator circuit in Which the amplitude of oscillations is controlled, comprising an electron discharge device having an anode, an oscillator grid, an auxiliary grid, and a cathode; a tuned circuit coupled to said anode, oscillator grid, and cathode for producing oscillations; a circuit coupled to said cathode and oscillator grid for developing a direct current voltage from the produced oscillations; and a feed-back path including a filter from said last circuit to said auxiliary grid to control the mutual conductance of said device in accordance with the direct current voltage developed in said last circuit, said filter comprising the series combin-ation of an inductance coil and a resistance connected between said auxiliary grid and said oscillator grid, and a condenser connecting said auxiliary grid and cathode,

14. A self-excited oscillator circuit in which the amplitude of oscillations is controlled, comprising an electron discharge device having an anode, an oscillator grid, an auxiliary grid, and a, cathode; a tuned circuit coupled to said anode, oscillator grid, and cathode for producing oscillations; a circuit coupled to said cathode and oscillator grid for developing a direct current voltage from the produced oscillations; and a feed-back path including a filter from said last circuit to said auxiliary grid to control the mutual conductance of said device in accordance with the direct current voltage developed in said last circuit, said filter including a condenser connected between said auxiliary grid and cathode for by-passing energy of the oscillator frequency.

15. The combination with a self-excited oscillator circuit in which the amplitude of oscillations is controlled, comprising an electron discharge device having an anode, an oscillator grid, an auxiliary grid, and a cathode; a tuned circuit having one terminal coupled to said anode, another terminal coupled to said oscillator grid, and an intermediate terminal thereon coupled to said cathode to produce oscillations; a resistance connected between said oscillator grid and a point of relatively fixed radio frequency potential for developing a direct current voltage therein; an electrically conductive connection between a point on said resistance and said [auxiliary grid for feeding back a portion of the developed direct current voltage, whereby the mutual conductance of said device is controlled in accordance with said voltage, and a filter comprising an inductance coil in series with a resistance inserted in said connection, of a source of relatively low frequency alternating current voltage connected between said cathode and the junction point of said coil and resistance for modulating the oscillations produced by said oscillator.

16. A self-excited oscillator circuit comprising an electron discharge device having an anode, a cathode, and first, second and third grids; a source of voltage supply conductively connected between said anode and cathode, a tuned circuit coupled to said anode, cathode and first grid in such manner as to produce oscillations; said tuned circuit having a coil connected between said anode and one side of said voltage supply, and a condenser connected between said anode and the other side of said voltage supply; a con nection from said second grid to said cathode; a resistance connected between said first grid and a point of substantially fixed radio frequency potential; an antenna coupled to said first grid, a resistor connected between said first resistance and said third grid, and a condenser connected between said third grid and cathode, whereby the mutual conductance of said device is controlled in accordance with the direct current voltage developed on said first grid and the intensity of oscillations controlled by the capacity between said antenna and said point of fixed radio frequency potential.

17. A self-excited oscillator circuit comprising an electron discharge device having an anode, a cathode, and first, second and third grids; a source of voltage supply conductively connected between said anode and cathode, a tuned circuit coupled to said anode, cathode and first grid in such manner as to produce oscillations; said tuned circuit having a coil connected between said anode and one side of said voltage supply, and a condenser connected between said anode and the other side of said voltage supply; a connection from said second grid to said cathode; a resistance connected between said first grid and a point of substantially fixed radio frequency potential; an antenna coupled to said first grid, a conductive connection including an impedance from said resistance to said third grid, a condenser connected between said anode and the junction point of said resistance and impedance,

whereby the mutual conductance of said device is controlled in accordance with the direct current voltage developed on said first grid and the intensity of oscillations controlled by the capacity between said antenna and said point of fixed radio frequency potential.

18. A self-excited oscillator circuit comprising an electron discharge device having an anode, a cathode, and first, second and third grids; a source of voltage supply conductively connected between said anode and cathode, a tuned circuit coupled to said anode, cathode and first grid in such manner as to produce oscillations; said tuned circuit having one terminal coupled to said first grid, another terminal coupled to said anode, and an intermediate terminal coupled to said cathode for producing oscillations; an antenna coupled to said first grid; a connection from said second grid to said cathode; and means for rectifying a portion of the oscillations produced in said tuned circuit and feeding said rectified portion back to said third grid for controlling the mutual conductance of said device.

19. A self-excited oscillator circuit comprising an electron discharge device having an anode, a cathode, and first, second and third grids; a source of voltage supply conductively connected between said anode and cathode, a tuned circuit coupled to said anode, cathode and first grid in such manner as to produce oscillations; said tuned circuit having one terminal capacitively coupled to said first grid, another terminal capacitively coupled to said anode, and an intermediate terminal coupled to said cathode for producing oscillations; an impedance connected between said first grid and cathode; an antenna coupled to said first grid; a connection from said second grid to said cathode; and means for rectifying a portion of the oscillations produced in 40 said tuned circuit and feeding said rectified portion back to said third grid for controlling the mutual conductance of said device.

20. A self-balancing capacity-operated relay comprising an oscillator circuit constituted by 45 an electron discharge device having an anode, a cathode, and first and second grids; a source of voltage supply conductively connected between said anode and cathode, a tuned circuit coupled to said anode, cathode and first grid in such 50 manner as to produce oscillations; said tuned circuit having one terminal capacitively coupled to said first grid, another terminal capacitively coupled to said anode, and an intermediate terminal coupled to said cathode for producing os- 5 cillations; a connection from one terminal of said tuned circuit to ground; an antenna coupled to said first grid; whereby said cathode fluctuates at a radio frequency potential, and feedback for said oscillator is determined by the difference in 60 ratio between the inductances of said tuned circuit on both sides of said intermediate terminal and the ratio between antenna-to-ground capacity and the capacity between said first grid and said tuned circuit, an output electron discharge device having a grid and an anode, a grid-leak between said last grid and said second grid of said oscillator, a by-pass connection for high frequency energy from said grid of said output device to the cathode of said oscillator, and circuit connections between said output device and said oscillator for causing said output device to rectify oscillations from said oscillator and to supply a negative charge on said second grid, and a relay coupled to the anode of said 75 output device.

'said antenna and said 21. In combination, a self-excited oscillator circuit in which the amplitude of oscillations is controlled, comprising an electron discharge device having an anode electrode, an oscillator grid electrode, an auxiliary grid electrode, and a cathode electrode; a tuned circuit coupled to said anode, cathode and oscillator grid electrodes in such manner as to produce oscillations; a circuit coupled to said cathode and one of said other electrodes for developing a direct current voltage from the produced oscillations in said tuned circuit, means for feeding back a part of said developed direct current voltage to said auxiliary electrode for varying the mutual conductance of said device; a path of low impedance to energy of the oscillator frequency connected between said auxiliary grid and said cathode; and a source of relatively low frequency modulation coupled to said auxiliary grid.

22. A self-excited oscillator circuit comprising an electron discharge device having an anode, a cathode, and first, second and third grids; a source of voltage supply conductively connected between said anode and cathode, a tuned circuit coupled to said anode, cathode and first grid in such manner as to produce oscillations; said tuned circuit having a coil connected between said anode and one side of said voltage supply, and a condenser connected between said anode and the other side of said voltage supply; a connection from said second grid to a point on said coil intermediate its ends; a condenser between said second grid and cathode; a resistance connected between said first, grid and a point of substantially fixed radio frequency potential; an antenna coupled to said first grid, a conductive connection including an impedance from said resistance to said third grid, whereby the mutual conductance of said device is controlled in ac cordance with the direct current voltage developed on said first grid and the intensity of oscillations controlled by the capacity between point of fixed radio frequency potential.

23. In combination, a self-excited oscillator circuit in which the amplitude of oscillations is controlled, comprising an electron discharge device having an anode electrode, an oscillator grid electrode, an auxiliary grid electrode, and a cathode electrode; a tuned circuit coupled to said anode, cathode and oscillator grid electrodes in such manner as to produce oscillations; a circuit coupled to said cathode and one of said other electrodes for developing a direct current voltage from the produced oscillations in said tuned circuit, means for feeding back a part of said developed direct current voltage to said auxiliary electrode for varying the mutual conductance of said device; a filter including a path of low impedance to energy of the oscillator frequency, said path being connected between said auxiliary grid and said cathode, and a source of relatively low frequency modulation coupled to a point on said filter intermediate the terminals thereof.

24. In combination, a self-excited oscillator circuit in which the amplitude of oscillations is controlled, comprising an electron discharge device having an anode electrode, an oscillator grid electrode, an auxiliary grid electrode, and a cathode electrode; a tuned circuit coupled to said anode, cathode and oscillator grid electrodes in such manner as to produce oscillations; a circuit coupled to said cathode and one of said other electrodes for developing a direct current voltage from the produced oscillations in said tuned circuit, means for feeding back a part of said developed direct current voltage to said auxiliary electrode for varying the mutual conductance of said device; a filter including a path of low impedance to energy of the oscillator frequency, said path being connected between said auxiliary grid and said cathode, and a source of relatively low frequency modulation coupled to a point on said filter intermediate the terminals thereof, the speed at which said direct current voltage is applied to said auxiliary grid being limited by the time constant of the elements of said filter and by the value of said path of low impedance, whereby said source of modulation produces no appreciable effect on the average output oscillation intensity.

25. A self-excited oscillator circuit comprising an electron discharge device having an anode, a cathode, and first and second grids, a tuned circuit including an inductance coil coupled to said anode, cathode and first grid in such manner as to produce oscillations, said anode being directly connected to one terminal of said inductance coil, said first grid being capacitively coupled to the other terminal of said inductance coil, and said cathode being capacitively coupled to an intermediate point on said inductance coil, a source of voltage supply having its positive terminal connected to said anode through said inductance coil of said tuned circuit and its negative terminal connected to said cathode through another inductance coil, an antenna coupled to said first grid, means coupled to said cathode and first grid for developing a direct current voltage from the produced oscillations in said tuned circuit, and a connection from said means to said second grid for controlling the mutual conductance of said device from said developed direct current voltage.

FRANCIS H. SHEPARD, JR. 

